Question

Assertion (A) : The backbone of DNA and RNA molecules is a chain consisting of heterocyclic base, pentose sugar and phosphate group. Reason (R) : Nucleotides and nucleosides mainly differ from each other in presence of phosphate group.

Nucleotides are joined together by

Ribose and 2-deoxyribose have an important role in biology. Among the most important derivatives are those with phosphate groups attached at the 5 position. Mono-, di- and tri-phosphate forms are important, as well as 3-5 cyclic monophosphates. Purines and pyrimidines form an important class of compounds with ribose and deoxyribose. When these purine and pyrimidine derivatives are coupled to a ribose sugar, they are called nucleosides.

Define the following terms :